The generation of electrical power is a complex matter which is dependent in part on the amount of power required on the grid. Therefore, the amount of power being generated varies widely depending on the time of day, day of the week, and atmospheric conditions such as cold spells and heat waves. While the amount of power varies, it is recognized that maximum efficiencies are achieved by operating power generation systems at a steady state or near steady state conditions. With this in mind, there has been an increased use of gas turbine systems that may be added online to the grid to provide additional power in that gas turbine systems typically are well suited for ease of being brought online quickly therefore being either in a standby or running mode. However, gas turbines are recognized as being not as efficient as other plant systems such as large steam plants because of the gas turbine system being an open cycle where approximately 60 to 70 percent of the energy is lost in waste heat energy.
One method of increasing efficiency that has been recognized is a combined cycle power plant in which a gas turbine, also referred to as a topping cycle, transfers its exhaust waste heat through a heat recovery system to a closed cycle heat engine such as a steam turbine. To capture the exhaust steam energy in these steam turbines, the steam turbine operates in a closed cycle that adds a circulating water system, a condensate water system, and a large cooling trap to reject the low energy heat.
The invention relates to a combined cycle system having an open cycle system using a fuel to create power and expending an exhaust with a waste heat. The system has a heat recovery exchanger for transferring heat from the exhaust with waste heat to the heat exchange fluid. A second open cycle system uses the heat exchange fluid to create power and expend the heat exchange fluid.
In one embodiment, the first open cycle system is a gas turbine, the second open cycle system is a steam turbine. The heat exchange fluid is water in a fluid and gaseous state. A pump moves and pressurizes the water to the heat recovery exchanger.
In one embodiment, an exhaust system combines the exhaust from the first open cycle and the heat exchange fluid from the second open cycle.
In one embodiment, the heat recovery exchanger is a once-through exchanger. In another embodiment, the heat recovery exchanger is a drum boiler. A purifier cleans the water prior to entering the heat recovery exchanger to remove dissolved minerals.
The steam turbine in the combined cycle system produces power in a range of between 30 to 45 percent of the power produced by the gas turbine. In one embodiment, the power produced is approximately 35 percent of the power produced by the gas turbine.
A dual-fluid heat engine has a gas turbine and a steam turbine. The gas turbine has a compressor section, a combustion chamber section, and a hot expansion turbine section. The compressor section compresses a first working fluid. The combustion chamber section is in fluid communication with the compressor outlet and mixes the air with the fuel to ignite and produce a hot first working fluid. The turbine section of the gas turbine has an inlet in fluid communication with the combustion chamber section for performing work by expansion of the first working fluid. In addition to producing mechanical energy, the gas turbine expends an exhaust fluid.
The steam turbine is an atmospheric exhaust expansion steam turbine. The steam turbine extracts energy from the heated second working fluid, steam, to drive a shaft to produce mechanical energy.
A heat recovery exchanger is coupled to the gas turbine exhaust and has a heat recovery inlet and an outlet for heating the second working fluid, water. The heat recovery exchanger extracts heat from the gas turbine exhaust to heat the water to produce water in a gaseous state, steam. A pump increases the pressure of the second working fluid prior to entrance into the heat recovery exchanger.
The steam turbine, likewise expends an exhaust in addition to producing mechanical energy. An exhaust chimney takes the gas turbine exhaust and the steam turbine exhaust, steam, and combines and rejects the exhausts into the atmosphere. The mechanical energy produced by both the gas turbine and the steam turbine drive electric generators.
The foregoing and other features and advantages of the system and method of the invention will be apparent from the following more particular description of preferred embodiments of the system and method as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views.